LARGE HEPATITIS-DELTA ANTIGEN IN PACKAGING AND REPLICATION INHIBITION- ROLE OF THE CARBOXYL-TERMINAL-19 AMINO-ACIDS AND AMINO-TERMINAL SEQUENCES

Hepatitis delta virus (HDV) encodes two proteins, the small delta anti gen (SHDAg) and large delta antigen (LHDAg). The latter is identical t o the former except for the presence of additional 19 amino acids at t he C terminus. While SHDAg is required for HDV replication, LHDAg inhi bits replication and, together with hepatitis B surface antigen (HBsAg ), is required for the assembly of HDV. The last 19 C-terminal amino a cids of LHDAg are essential for HDV assembly, Most of LHDAg (amino aci ds 19 to 146 and 163 to 195) had been shown to be dispensable for pack aging with HBsAg. To discern whether the last 19 C-terminal amino acid s solely constitute the signal for packaging with HBsAg, we constructe d two LHDAg deletion mutants and tested their abilities to be packaged with HBsAg in cotransfection experiments. We found that deletion of a mino acids 2 to 21 and 142 to 165 did not affect LHDAg packaging. This result suggested that only the last 19 C-terminal amino acids of LHDA g are required for packaging. We further constructed two plasmids whic h expressed c-H-ras with or without additional 19 C-terminal amino aci ds identical to those in LHDAg. Only c-a-ras with additional 19 amino acids could be cosecreted with HBsAg in the cotransfection experiment, This result confirmed that the C-terminal 19 amino acids are the pack aging signal for HBsAg. We also tested the trans activation activity a nd trans-dominant inhibitory activity of the deletion mutants of SHDAg and LHDAg, respectively, In contrast to deletion of amino acids 142 t o 165, deletion of amino acids 2 to 21 impaired the trans-dominant inh ibitory activity of LHDAg. Deletion of amino adds 2 to 21 and 142 to 1 65 did not affect the trans activation activity of SHDAg. This result suggested that a functional domain which is important for the trans-do minant inhibitory activity of LHDAg exists in the amino terminus of HD Ag.